Multi-channel transmitter optical subassembly (tosa) with opposing placement of transistor outline (to) can laser packages

ABSTRACT

A multi-channel transmitter optical subassembly (TOSA) including staggered transistor outline (TO) can laser package placement to provide enhanced coupling and optical power is disclosed, and may be used in an optical transceiver for transmitting an optical signal. The TOSA comprises a housing that includes plurality of sidewall openings with each sidewall opening configured to couple to a TO can laser package to provide coarse wavelength division multiplexing. The housing includes at least first and second sidewall openings on a first sidewall, and a third sidewall opening disposed on a sidewall opposing the first sidewall and being positioned at generally a mid-point between the first and second sidewall openings. This staggered and opposing sidewall opening arrangement allows an increased distance between adjacent sidewall openings, and thus, the TOSA may increase optical power and yield by providing additional space for performing post-attachment alignment of TO can laser packages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. application Ser. No. ______ (Attorney Docket No. PAT257US) titled “Receiver Optical Subassembly Housing With Sidewall Receptacle To Provide Electrical Isolation Between An Adjacent Transmitter Optical Subassembly in a Transceiver Housing” filed concurrently herewith, which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to laser packages, and more particularly, to a transmitter optical subassembly (TOSA) with opposing placement of transistor outline (TO) can laser packages for coarse wavelength division multiplexing (CWDM) for use in an optical transceiver.

BACKGROUND INFORMATION

Optical transceivers are used to transmit and receive optical signals for various applications including, without limitation, internet data center, cable TV broadband, and fiber to the home (FTTH) applications. Optical transceivers provide higher speeds and bandwidth over longer distances, for example, as compared to transmission over copper cables. The desire to provide higher speeds in smaller optical transceiver modules for a lower cost has presented challenges, for example, with respect to maintaining optical efficiency (power), thermal management, insertion loss, and manufacturing yield.

Optical transceiver modules can include one or more transmitter optical subassemblies (TOSAs) and receiver optical subassemblies (ROSAs). TOSAs, for example, can include a plurality of transistor outline (TO) can laser packages, and can also provide electrical connections and optical couplings to the laser diode within those laser packages. One technique for fixedly attaching a TO can laser package to TOSA housing includes using laser welding. During the welding process, however, rapid solidification of a welded region and associated material shrinkage may cause post-weld-shift (PWS). PWS, even in the order of a few micrometers, can result in total loss of optical power. Techniques for correction of PWS can include so-called “laser hammering” that seeks to counteract misalignment through additional laser welds to “hammer” fibers into an optimized alignment. This is accomplished, essentially, by adding additional successive laser welds in particular locations to use the effects of PWS to “pull” fibers out of misalignment. A light measurement may be taken between each successive weld to determine a resulting optical power. Correction of PWS has become increasingly more complex and expensive during manufacturing because optical transceivers continue to scale down in size, and in particular, have less area available for laser welding/attachment of laser packages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood by reading the following detailed description, taken together with the drawings wherein:

FIG. 1 is a perspective view of one approach to a multi-channel TOSA with multiple TO can laser packages.

FIG. 2 schematically illustrates an embodiment of an optical transceiver including a multi-channel TOSA and multi-channel receiver optical subassembly (ROSA).

FIG. 3 is a perspective view of an example small form-factor (SFF) pluggable transceiver with a multi-channel TOSA including TO can laser packages and a multi-channel ROSA, in accordance with an embodiment of the present disclosure.

FIG. 4A is a perspective view of an embodiment of the multi-channel TOSA for use in the optical transceiver module shown in FIG. 3.

FIG. 4B is a cross-sectional view of the multi-channel TOSA of FIG. 4A, in accordance with an embodiment of the present disclosure.

FIG. 5 shows an exploded view of the multi-channel TOSA of FIGS. 3-4B, in accordance with an embodiment of the present disclosure.

FIGS. 6A and 6B show perspective views of a first sidewall and second sidewall of the multi-channel TOSA of FIGS. 3-4B, respectively, in accordance with an embodiment of the present disclosure.

FIG. 7 shows a perspective view of one example TO can laser package for use in the multi-channel TOSA of FIGS. 3-5.

DETAILED DESCRIPTION

A multi-channel transmitter optical subassembly (TOSA) including staggered TO laser can package placement to provide enhanced coupling and optical power is disclosed, and may be used in an optical transceiver for transmitting an optical signal at multiple different channel wavelengths. The TOSA comprises a housing made of metal or other thermally conductive material, and includes a plurality of sidewall openings disposed thereon. Each sidewall opening is configured to couple to TO can laser packages and provide coarse wavelength division multiplexing (CWDM). The housing includes at least a first and second sidewall opening on a first sidewall of the housing, and a third sidewall opening disposed on an opposite sidewall opposing the first and second sidewall opening. The third sidewall opening is positioned at generally a mid-point between the first and second sidewall openings such that an axis extending tangent from the third sidewall opening contacts the second and third sidewall opening. The first and second sidewall openings are separated by a distance generally equal to at least half the diameter of each of the respective sidewall openings. This staggered and opposing sidewall opening arrangement allows an increased distance between adjacent sidewall openings, without reducing the channel allocation for the TOSA. Thus the multi-channel TOSA provides additional space for performing post-attachment alignment of TO can laser packages through laser hammering, and other such alignment techniques, which simplifies those attachment/alignment processes to reduce error rates, and increase yield.

As previously discussed, optical components such as TOSAs continue to scale down in size, and as a result, face numerous non-trivial issues related to maintaining optical power, yield, and reliability. For example, FIG. 1 shows one example of a multi-channel TOSA 100 compatible with a Small Form-factor Pluggable (SFFP) transceiver. As shown the multi-channel TOSA 100 includes four (4) TO can laser packages 104 arranged on an upper side-wall of housing 102, thus providing 4 wavelengths/channels for CWDM. To comport with form factor requirements governed by SFFP standards, such as the Quad Small Form-factor Pluggable (QSFP) standard, the distance between adjacent TO can laser packages 104 is relatively small with dimension 106 being generally 0.1 mm. This means that the approach chosen to fixedly attach TO can laser packages 104 must effectively operate within this relatively small dimension with little room for error.

One suitable approach to fixedly attaching TO can laser packages includes laser welding using a pulsed neodymium-doped yttrium aluminium garnet (Nd:YAG) laser. A Nd:YAG laser can achieve optical alignment and with submicron tolerances over the lifetime of the TOSA 100, but manufacturing is complex using such a laser due to the small dimension 106 between TO can laser packages 104. For example, as shown by angle θ, a laser welding system has approximately 87°±1° relative to the surface of the house 102 to generate welds. To correct for misalignment caused by PWS and to bring TO can laser packages 104 into optical alignment, additional successive welds are added at specific positions, which is generally referred to as laser hammering. When those welds fall within dimension 106, for example, the welding process is more complex and time consuming. In a more general sense, the cost and time associated with each manufacturing TOSA 100 is increased by the relatively tiny tolerances afforded by dimension 106.

Thus, in accordance with an embodiment, a multi-channel TOSA including staggered TO can laser package placement to provide additional space between adjacent TO can laser packages is provided herein. In some cases, the multi-channel TOSA disclosed herein includes at least twice the distance between adjacent TO can laser packages versus other TOSA approaches, such as the one shown in FIG. 1, thus providing additional space, and importantly, a wide-range of angles in which to perform initial laser welds and subsequent “hammer” welds to ensure optimized optical alignment. The multi-channel TOSA disclosed herein can be utilized within, for example, transceivers that implement QSFP standards (e.g., 40 GB-LR), and other similarly constrained or otherwise small form-factor transceivers.

As used herein, “channel wavelengths” refer to the wavelengths associated with optical channels and may include a specified wavelength band around a center wavelength. In one example, the channel wavelengths may be defined by an International Telecommunication (ITU) standard such as the ITU-T dense wavelength division multiplexing (DWDM) grid. The term “coupled” as used herein refers to any connection, coupling, link or the like and “optically coupled” refers to coupling such that light from one element is imparted to another element. Such “coupled” devices are not necessarily directly connected to one another and may be separated by intermediate components or devices that may manipulate or modify such signals.

Now turning to FIG. 2 there is an optical transceiver 200 consistent with embodiments of the present disclosure. In more detail, the optical transceiver 200 transmits and receives four (4) channels using four different channel wavelengths (λ₁, λ₂, λ₃, λ₄) and may be capable of transmission rates of at least about 10 Gbps per channel. In one example, the channel wavelengths λ₁, λ₂, λ₃, λ₄ may be 1270 nm, 1290 nm, 1080 nm, and 1330 nm, respectively. The optical transceiver 200 may also be capable of transmission distances of 2 km to at least about 10 km. The optical transceiver 200 may be used, for example, in internet data center applications or fiber to the home (FTTH) applications. In an embodiment, the optical transceiver 200 implements the specification SFF-8436 titled “QSFP+ 10 Gbs 4× PLUGGABLE TRANSCEIVER Rev 4.8” (hereinafter QSFP+), published on Oct. 31, 2013 by the Electronic Industries Alliance (EIA).

This embodiment of the optical transceiver 200 includes a multi-channel TOSA 302 for transmitting optical signals on different channel wavelengths and a multi-channel receiver optical subassembly (ROSA) 230 for receiving optical signals on different channel wavelengths. The multi-channel TOSA 302 and the multi-channel ROSA 230 are located in a transceiver housing 202. A transmit connecting circuit 204 and a receive connecting circuit 208 provide electrical connections to the multi-channel TOSA 302 and the multi-channel ROSA 230, respectively, within the housing 202 and communicate with external systems via data bus 203. In some cases, data bus 203 is a 38-pin connector that comports with physical connector QSFP standards and data communication protocols.

In any event, the transmit connecting circuit 204 is electrically connected to the electronic components (e.g., TO can laser packages) in the multi-channel TOSA 302, and the receive connecting circuit 208 is electrically connected to the electronic components (e.g., the photodiode packages) in the multi-channel ROSA 230. The transmit connecting circuit 204 and the receive connecting circuit 208 include at least conductive paths to provide electrical connections and may also include additional circuitry. The multi-channel TOSA 302 transmits and multiplexes multiple channel wavelengths and is coupled to an optical interface port 212. The optical interface port 212 may comprise an LC connector receptacle, although other connector types are also within the scope of this disclosure. For example, the optical interface port 212 may comprise a multi-fiber push on (MPO) connector receptacle.

In cases where the optical interface port 212 comprises a duplex, or bi-directional, LC receptacle, the LC connector receptacle provides optical connections to the multi-channel TOSA 302, and provides optical connections to the multi-channel ROSA 230. The LC connector receptacle may be configured to receive and be coupled to a mating LC connector 214 such that the transmit optical fiber 222 of the external fibers 224 optically couples to the multi-channel TOSA 302, and the receive optical fiber 217 of the external fibers 224 optically couples to the multi-channel ROSA 230.

The multi-channel TOSA 302 includes multiple TO can laser packages, discussed in greater detail below, and optics for producing assigned channel wavelengths and coupling the same into the transmit optical fiber 222. In particular, the lasers in the multi-channel TOSA 302 convert electrical data signals (TX_D1 to TX_D4) received via the transmit connecting circuit 204 into modulated optical signals transmitted over the transmit optical fiber 222. The lasers may include, for example, distributed feedback (DFB) lasers with diffraction gratings. The multi-channel TOSA 302 may also include monitor photodiodes for monitoring the light emitted by the lasers. The multi-channel TOSA 302 may further include one or more temperature control devices, such as a resistive heater and/or a thermoelectric cooler (TEC), for controlling a temperature of the lasers, for example, to control or stabilize the laser wavelengths.

The multi-channel ROSA 230 includes, for example, photodiodes, mirrors and filters that can de-multiplex different channel wavelengths in a received optical signal. The multi-channel ROSA 230 can detect, amplify, and convert such optical signals received from the external optical fibers 224, and can provide the converted optical signals as electrical data signals (RX_D1 to RX_D4) that are output via the receive connecting circuit 208.

This embodiment of the optical transceiver 200 includes 4 channels and may be configured for coarse wavelength division multiplexing (CWDM), although other numbers of channels are possible.

Referring to FIG. 3, an example small form-factor (SFF) pluggable optical transceiver 300 with a multi-channel TOSA including TO can laser packages and multi-channel ROSA is described and shown in greater detail. The embodiment shown in FIG. 3 is one example of the optical transceiver 200 of FIG. 2 implemented in a small form-factor. For example, the optical transceiver 300 may implement the QSFP+ specification. The optical transceiver 300 includes the transceiver housing 202, a multi-channel TOSA 302 in one region of the housing 202, and a multi-channel ROSA 230 located in another region of the housing 202. As shown, the TO can laser package 304c of the multi-channel TOSA 302 directly contacts a surface of the ROSA 230. The multi-channel TOSA 302 is electrically connected to transmit flexible printed circuits (FPCs) 304 and optically coupled to the LC connector port 212 at an end of the housing 202. The multi-channel ROSA 230 is electrically connected to a receive flexible printed circuit (FPC) 309 and optically coupled to the LC connector port 212 at the end of the housing 202.

The multi-channel TOSA 302 includes TO can laser packages 304 a, 304 b, 304 c, and 304 d, with each containing optical components such as a laser diode. The TO can laser packages can provide, for example, output power from 1.85 mW to 2 W, although other output power is within the scope of this disclosure. The TO can laser packages may provide a broad spectrum of channel wavelengths, or configured to provide a relatively narrow spectrum of channel wavelengths such as a single channel wavelength. In some cases, the TO can laser packages provide center wavelengths 375 nm to 1650 nm, for example. In an embodiment, the TO can laser packages are Ø3.8 mm, Ø5.6 mm, or Ø9 mm TO cans, although other configurations are also within the scope of this disclosure. For instance, the TO can laser packages can include Ø9.5 mm and TO-46 cans.

One specific example of a TO can laser package 700 is shown in FIG. 7. As shown, the TO can laser package 700 includes a housing 702, connector pins 704, and a header 706 with a laser diode 708. The connector pins 704 couple to the transmit FPC 304, and the multi-channel TOSA 302 optically couples an associated channel wavelength of the laser diode 708 to the transmit optical fiber 222 of the external fibers 224 (FIG. 2) via collimating lenses, filters, and other optics such as a focusing lens, as discussed in greater detail below with reference to FIG. 4B.

Returning to FIG. 3, the multi-channel TOSA 302 includes TO can laser packages 304 a-304 d fixedly attached in a staggered manner, with TO can laser package 304 c being disposed on opposing sidewall to that of TO can laser packages 304 a and 304 b, as discussed in greater detail below.

Referring to FIG. 4A, one embodiment of a multi-channel TOSA 302 for use in the optical transceiver module shown in FIG. 3 is shown in greater detail. As shown, the multi-channel TOSA 302 includes a housing 202 with first and second sidewalls 308 and 310, respectively, positioned on opposite sides of the housing 202 and extending generally in parallel along a first major axis 303 from a first end 326 to a second end 327, and forming a compartment defined by an inner surface within the housing 202. The first sidewall 308 includes at least first and second sidewall openings 404 a and 404 b (also shown with additional detail in FIG. 5) and the second sidewall 310 includes at least a third sidewall opening 404 c being positioned generally at a midpoint 307 located between the sidewall openings 404 a and 404 b of the first sidewall 308. The multi-channel TOSA 302 includes first and second TO can laser packages 304 a and 304 b fixedly attached to the first and second openings 404 a and 404 b of the first sidewall 308, respectively, and a third TO can laser package 304 c fixedly attached to the third sidewall opening 404 c opposing the first and second TO can laser packages 304 a and 304 b. The housing 202 further includes an end sidewall 312 at the first end 326 and adjoining the first and second sidewalls 308 and 310, the end sidewall 312 including a fourth sidewall opening 404 d and a fourth TO can laser package 304 d fixedly attached thereto.

As shown, the dimension 306 includes a distance of at least about 3 mm along the surface of the first sidewall 308 between adjacent TO can laser packages 304 a and 304 b. In some cases, dimension 306 includes a length of 2 mm to 5 mm, for example. As will be appreciated in light of this disclosure, dimension 306 departs from other TOSA approaches, such as discussed above with regard to FIG. 1, that have a minimal spacing between TO can laser packages. This increased dimension 306 advantageously allows laser welds to be formed without the cost and complexity normally associated with having tight tolerances between laser packages. For example, and as shown in FIG. 4A, angle θ is generally 30° relative to the housing 202. This means that laser welding systems can perform welding at multiple angles from, for example, 30° tot 36°, for example. In other cases, the angle θ allows laser welding systems to weld at less than 30°.

Referring to FIG. 4B, there is a cross-sectional view of the multi-channel TOSA 302 of FIG. 3. As shown, the housing 202 also forms an internal cavity 316, or compartment, that defines a light path 322 that extends through filters 318 a, 318 b and 318 c, respectively, before encountering focusing lens 320. The filters 318 a-318 c are positioned on filter holders 319 a, 319 b, and 319 c, respectively. An optical coupling receptacle 324 extends from the second end 327 for optically coupling the light of TO can laser packages 304 a-304 d to the transmit optical fiber 222. Thus the filters 318 a-318 d, the lens 320, the optical coupling receptacle 324 are generally aligned or positioned along a longitudinal axis provided by the light path 322. This combination of filters may be accurately described as multiplexing optics and can provide coarse wavelength division multiplexing (CWDM) in an optical signal. Multiplexing different channel wavelengths using this configuration will now be discussed in the context of a four (4) channel TOSA configuration, such as shown in FIG. 4B.

Each of the TO can laser packages 304 a-304 d can be associated with different channel wavelengths. For example, the channel wavelengths (λ1, λ2, λ3, λ4) associated with TO can laser packages 304 a-304 d may be 1290 nm, 1330 nm, 1310 nm, and 1270 nm, respectively. To multiplex these different channel wavelengths into a signal optically coupled to transmit optical fiber 222, the housing includes TO can laser package 304 d configured to direct light coaxially along light path 322 into the compartment 316. In turn, the filter 318 a positioned adjacent the TO can laser package 304 d can provide wavelength-dependent transmission such that only the channel wavelength λ1, associated with the TO can laser package 304 d, pass through filter 318 a. The filter 318 a may also provide wavelength-dependent reflectivity such that only channel wavelength λ2 is reflected therefrom. At this point, the light along light path 322 includes, essentially, channel wavelengths λ1 and λ2. After those channel wavelengths pass through filter 318 c, they converge with wavelength λ3, which is provided by the filter 318 c reflecting only channel wavelength λ3 from the light directed by TO laser package 304 c. At this point the light along light path 322 now includes, essentially, channel wavelengths λ1, λ2 and λ3. After those channel wavelengths pass through filter 318 b, they converge with channel wavelength λ4, which is provided by the filter 318 b reflecting only channel wavelength λ4 from the light directed by TO laser package 304 b. As shown, collimating lenses 305 a-305 d collimate light emitted by each TO can laser package. Thus at focusing lens 320, the resulting optical signal includes multiple different multiplexed channel wavelengths (e.g., λ1, λ2, λ3, λ4) and is optically coupled to the transmit optical fiber 222.

As should be appreciated, the multi-channel TOSA 302 may include additional channels and is not necessarily limited to the four (4) shown in FIG. 4B. That is, additional TO can laser packages may be disposed along the sidewalls of housing 202. For instance, the first sidewall 308 may include 3 or more TO can laser packages. Each of those TO can laser packages may be disposed with spacing similar to the embodiment shown in FIG. 4B. On the opposing sidewall, such as second sidewall 310, TO can laser packages may be fixedly attached such that they are disposed generally coextensive or otherwise overlapping with the area between each of the TO can laser packages of the first sidewall 308. This staggered/opposing arrangement may be repeated for N number of optical channels, depending on a desired configuration.

Moreover, it should be appreciated in light of this disclosure that placement of the TO can laser packages are not necessarily limited to the embodiment shown. For example, TO can laser package 304 c may be fixedly attached to a sidewall that is perpendicular (or at a right angle) to the TO can laser packages 304 a and 304 b.

Referring now to FIG. 5, there is an exploded view of the multi-channel TOSA 302, in accordance with an embodiment of the present disclosure. As shown, each of the TO can laser packages 304 a-304 d include an associated welding ring 402 a, 402 b, 402 c, and 402 d, respectively. These welding rings 402 a-402 d allow the TO can laser packages 304 a-304 d to be placed over and fixedly attached to sidewall openings 404 a, 404 b, 404 c and 404 d, respectively. As previously discussed, laser welding is one approach that is particularly well suited for ensuring optical efficiency (power) and reliable operation over a lifetime of the multi-channel TOSA 302.

Note that an outer surface of the filter holder 319 b is substantially flat, and co-planar with an outer surface of the first sidewall 308. This advantageously provides a generally flat area that does not otherwise obstruct access when attaching TO can laser packages 304 a and 304 b during manufacturing. FIG. 6A further illustrates how filter holder 319 c resides between TO can laser packages 304 a and 304 b, but is coplanar or otherwise flat against the first sidewall 308. On the other hand, FIG. 6B illustrates how filter holders 319 a and 319 b are generally flat and also do not obstruct access to the area around TO can laser package 304 c along the second sidewall 310. As shown in FIG. 6A and 6B, the multi-channel TOSA 302 may have a relatively small size. In some embodiments, the long axis of the housing may be 15 mm, or less.

The multi-channel TOSA 302 may be formed as one piece or as multiple pieces attached together. Although the illustrated embodiment shows the multi-channel TOSA 302 with a particular shape, other shapes and configurations are also possible. In other embodiments, for example, the housing 202 may be generally cylindrical.

The increased distance between the TO can laser packages 304 a-304 d advantageously provides for increased tolerances when fixedly attaching the same to sidewall openings 404 a-404 d of the housing 202. This increased area allows for a laser welding system to have a wide-range of angles in which to generate welds, and thus, increase yield and reliability of the multi-channel TOSA 302 because of reduced error rates and faster time between establishing initial laser welds and optimizing optical efficiency through laser hammering. In addition, an increased surface area between TO can laser packages improves transfer or heat conduction, and thus, facilitates more effective heat dissipation than other approaches to TOSA packages (e.g., such as shown in FIG. 1).

Further Example Embodiments

In accordance with one aspect of the present disclosure, a transmitter optical subassembly (TOSA) including a plurality of transistor outline (TO) can laser packages is disclosed. The TOSA may comprise a housing including at least a first and second sidewall on opposite sides of the housing and extending along a first major axis from a first end to a second end, and forming a compartment defined by an inner surface therein, the first sidewall including at least first and second sidewall openings, the second sidewall including at least a third sidewall opening being positioned generally at a midpoint between the first and second sidewall openings, and at least first and second TO can laser packages fixedly attached to the first and second sidewall opening of the first sidewall, respectively, and a third TO can laser package fixedly attached to the third sidewall opening and opposing the first and second TO can laser packages.

In one aspect, the housing may further include a third sidewall at the first end and adjoining the first and second sidewall, the third sidewall including a fourth sidewall opening and a fourth TO can laser package fixedly attached thereto.

In one aspect, the TOSA may comprise a plurality of welding rings, wherein the plurality of TO can laser packages are fixedly attached to respective sidewalls of the housing by the plurality of welding rings via laser welds.

In one aspect, the compartment may define a light path, the light path extending from the first end to at least the second end.

In one aspect, each of the plurality of TO can laser packages may include a laser diode optically aligned to direct light into the compartment.

In one aspect, the TOSA may further comprise filters aligned with the TO can laser packages to pass and reflect laser light at associated channel wavelengths.

In one aspect, each filter may include an associated filter holder, each of the filter holders being fixedly attached to a sidewall of the housing and providing a substantially flat surface between adjacent TO can laser packages along an outer edge of the housing.

In one aspect, the compartment may include a focusing lens aligned with a light path at the second end of the housing.

In one aspect, the first and second TO can laser packages may be greater than 1 mm apart.

In one aspect, the second end may include an optical coupling receptacle configured to optically couple a signal having multiple different channel wavelengths to a transmit optical fiber.

In accordance with another aspect of the present disclosure, an optical transceiver module is disclosed. The optical transceiver may comprise a transceiver housing, a transmitter optical subassembly (TOSA) having a plurality of transistor outline (TO) can laser packages fixedly attached thereto and located in the transceiver housing for transmitting optical signals at different channel wavelengths, the TOSA comprising a housing including at least a first and second sidewall on opposite sides of the housing and extending along a first major axis from a first end to a second end, and forming a compartment defined by an inner surface therein, the first sidewall including at least first and second sidewall openings, the second sidewall including at least a third sidewall opening being positioned generally at a midpoint between the first and second sidewall openings, and at least first and second transistor outline TO can laser packages fixedly attached to the first and second sidewall opening of the first sidewall, respectively, and a third TO can laser package fixedly attached to the third sidewall opening and opposing the first and second TO can laser packages, a multi-channel receiver optical assembly (ROSA) located in the transceiver housing for receiving optical signals at different channel wavelengths.

In one aspect, the optical transceiver may further comprise a transmit connecting circuit electrically connected to the TOSA, and a receive connecting circuit electrically connected to the ROSA.

In one aspect, the TOSA may further comprise filters within the compartment configured to provide a multiplexed optical signal having multiple different wavelengths.

In one aspect, the TOSA may further comprise a third sidewall at the first end and adjoining the first and second sidewall, the third sidewall including a fourth sidewall opening and a fourth TO can laser package fixedly attached thereto.

In one aspect, each of the first, second, third and fourth TO can laser packages may be associated with a channel wavelength of 1290 nm, 1330 nm, 1310 nm, and 1270 nm, respectively.

In one aspect, the TOSA further may comprise a plurality of welding rings, wherein each of the plurality of TO can laser packages are fixedly attached to respective sidewalls of the TOSA housing by the plurality of welding rings via laser welds.

In one aspect, the transceiver may be a Quad Small Form-factor Pluggable (QSFP) transceiver module and the TOSA is configured to transmit at four different channel wavelengths at transmission rates of at least about 10 Gbps per channel and transmission distances of 2 km to at least about 10 km.

In one aspect, the third TO can laser package may directly contact a surface of the ROSA.

In one aspect, the first and second TO can laser packages of the TOSA may be greater than 1 mm apart.

In one aspect, the second end of the TOSA may include an optical coupling receptacle configured to optically couple a signal having multiple different channel wavelengths to a transmit optical fiber.

While the principles of the disclosure have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the disclosure. Other embodiments are contemplated within the scope of the present disclosure in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present disclosure, which is not to be limited except by the following claims. 

1. A transmitter optical subassembly (TOSA) including a plurality of transistor outline (TO) can laser packages, the TOSA comprising: a housing including at least a first and second sidewall on opposite sides of the housing and extending along a first major axis from a first end to a second end, and forming a compartment defined by an inner surface therein, the first sidewall including at least first and second sidewall openings, the second sidewall including at least a third sidewall opening being positioned generally at a midpoint between the first and second sidewall openings; at least first and second TO can laser packages coupled to the first and second sidewall opening of the first sidewall, respectively, and a third TO can laser package coupled to the third sidewall opening and opposing the first and second TO can laser packages; at least a first filter holder coupled to the first sidewall between the first and second sidewall openings of the first and second TO can laser packages, respectively, and wherein the first filter holder provides a substantially flat surface along an outer edge of the housing between the first and second TO can laser packages; and a first filter coupled to the first filter holder.
 2. The TOSA of claim 1, further comprising a third sidewall at the first end and adjoining the first and second sidewall, the third sidewall including a fourth sidewall opening and a fourth TO can laser package coupled thereto.
 3. The TOSA of claim 1, further comprising a plurality of welding rings, wherein the plurality of TO can laser packages are coupled to respective sidewalls of the housing by the plurality of welding rings via laser welds.
 4. The TOSA of claim 1, wherein the compartment defines a light path, the light path extending from the first end to at least the second end.
 5. The TOSA of claim 4, wherein each of the plurality of TO can laser packages includes a laser diode optically aligned to direct light into the compartment.
 6. The TOSA of claim 1, further comprising: a second and third filter holder coupled to the third sidewall on opposite sides of the third TO can laser packages relative to each other; and a second and a third filter coupled to the second and third filter holders, respectively, wherein each of the first, second and third filters are configured to align with an associated TO can laser package to pass and reflect laser light at associated channel wavelengths.
 7. The TOSA of claim 6, wherein each of the second and third filter holders provide a substantially flat surface along an outer edge of the housing.
 8. The TOSA of claim 1, wherein the compartment includes a focusing lens aligned with a light path at the second end of the housing.
 9. The TOSA of claim 1, wherein the first and second TO can laser packages are greater than 1 mm apart.
 10. The TOSA of claim 1, wherein the second end includes an optical coupling receptacle configured to optically couple a signal having multiple different channel wavelengths to a transmit optical fiber.
 11. An optical transceiver module comprising: a transceiver housing; a transmitter optical subassembly (TOSA) having a plurality of transistor outline (TO) can laser packages coupled thereto and located in the transceiver housing for transmitting optical signals at different channel wavelengths, the TOSA comprising: a housing including at least a first and second sidewall on opposite sides of the housing and extending along a first major axis from a first end to a second end, and forming a compartment defined by an inner surface therein, the first sidewall including at least first and second sidewall openings, the second sidewall including at least a third sidewall opening being positioned generally at a midpoint between the first and second sidewall openings; and at least first and second transistor outline TO can laser packages coupled to the first and second sidewall opening of the first sidewall, respectively, and a third TO can laser package coupled to the third sidewall opening and opposing the first and second TO can laser packages; a multi-channel receiver optical assembly (ROSA) located in the transceiver housing for receiving optical signals at different channel wavelengths; and wherein the third TO can laser package of the TOSA directly contacts a surface of the multi-channel ROSA.
 12. The optical transceiver of claim 11, further comprising a transmit connecting circuit electrically connected to the TOSA, and a receive connecting circuit electrically connected to the ROSA.
 13. The optical transceiver of claim 11, wherein the TOSA further comprises a plurality of filters within the compartment configured to provide a multiplexed optical signal having multiple different wavelengths.
 14. The optical transceiver of claim 11, wherein the TOSA further comprises a third sidewall at the first end and adjoining the first and second sidewall, the third sidewall including a fourth sidewall opening and a fourth TO can laser package coupled thereto.
 15. The optical transceiver of claim 14, wherein each of the first, second, third and fourth TO can laser packages are associated with a channel wavelength of 1290 nm, 1330 nm, 1310 nm, and 1270 nm, respectively.
 16. The optical transceiver of claim 11, the TOSA further comprises a plurality of welding rings, wherein each of the plurality of TO can laser packages are coupled to respective sidewalls of the TOSA housing by the plurality of welding rings via laser welds.
 17. The optical transceiver of claim 11, wherein the transceiver is a Quad Small Form-factor Pluggable (QSFP) transceiver module and the TOSA is configured to transmit at four different channel wavelengths at transmission rates of at least about 10 Gbps per channel and transmission distances of 2 km to at least about 10 km.
 18. (canceled)
 19. The optical transceiver of claim 11, wherein the first and second TO can laser packages of the TOSA are greater than 1 mm apart.
 20. The optical transceiver of claim 11, wherein the second end of the TOSA includes an optical coupling receptacle configured to optically couple a signal having multiple different channel wavelengths to a transmit optical fiber.
 21. The TOSA of claim 1, wherein the first sidewall includes a first step portion adjacent the first end of the housing that defines at least one surface, and wherein the substantially flat surface provided by the first filter holder along an outer edge of the housing is offset relative to the at least one surface defined by the first step portion.
 22. The TOSA of claim 21, wherein the third sidewall includes a second step portion adjacent the first end of the housing, the first and second step portions defining a tapered region that extends between the first and second ends of the housing. 